2002 Sierra Denali Quadrasteer Vibration

[outsidelinebacker]

Hey guys,

So I have a vibration that feels like it is coming through the seat. It does not happen consistently, but once it does, speed makes it more violent. I am having a hard time understanding it as it appears to happen after I have been driving for a while. Road surface may make a difference, but I doubt it. I checked U-joints and they are new or good on both drive shafts. I have not worried much about tires due to the symptoms, but they are OK. They may be worn enough for a rebalance. The only things I am doing differently from factory recommendations is running 54lbs in the front and 36lbs in the back. I do not think it is a tire problem as the drive train feels like it is shuddering, even when I am winding down. If it were tires, should it not happen all the time at certain speeds?
Today I ran 10 miles into the wind with nothing. Turned towards town in a cross wind and a sudden moderate vibration started. I backed off and I could still feel it at 35, only less pronounced. Get out of the dentist and come up to speed along the river OK. Cross the bridge and head down the blacktop. After I had put another 10 miles behind me away from town, here it comes again.
The weird thing is that as I was coming back home I noticed the "tow" light was dim or flickering. Maybe driving in 2 wheel steer mode would narrow the possibilities.

Please help,
Kevin

[KMGZ400]

I would start with balancing all 4 tires and getting a 4 wheel alignment

[outsidelinebacker]

That seems to be the next step from what I hear.

 

I really appreciate you taking the time to help me.

 

Thanks,

Kevin